Conventionally, as a network system for servo motors, for example, a system using the SERCOS interface (IEEE1491) has been known. This SERCOS interface is designed, as shown in FIG. 23, to synchronize the periodic operation of servo drive by transmitting a synchronous packet (sync-telegram) to the servo drive by using the interface in every control period of periodic control.
In the system using the SERCOS interface shown in FIG. 23, the control period of all servo drives (slaves) is synchronized by broadcasting the synchronous packet (sync-telegram) to all servo drives (slaves) periodically from the controller (master).
However, in the conventional system using the SERCOS interface, the precision of the control period is determined by the precision of periodic transmission of the synchronous packet (sync-telegram), and if transfer of a large packet is attempted at the same time as asynchronous communication between slaves, jitter occurs in the transmission period of the synchronous packet (sync-telegram), and packet transfer of large size or asynchronous communication between slaves cannot be achieved. Thus, flexibility is lacking.